A searing interferometer is means of visualizing a phase change of light, caused by a subject, using a shift of fringes. The fringes are generated by separating coherent light, such as beams irradiated from a single light source, generating distortion of wavefronts in one beam by the subject, and slightly shifting the other beam. This searing interferometer is used, for example, for improving the visibility of a subject in the field of phase contrast microscopes.
As a shearing interferometer, an interferometer using Talbot interferometry is known.
According to the Talbot interferometry, light from a light source is irradiated onto a subject, and light, of which phase is changed by transmitting through the subject, is guided to a diffraction grating. The light diffracted by the diffraction grating forms an interference pattern in a position that is a predetermined distance (Talbot distance) away from the diffraction grating. In the case of using an x-ray, directly detecting an interference pattern may be difficult, since the period of the interference pattern is very short. A method that is proposed to solve this problem is disposing an absorption grating in a position where the interference pattern is formed, generating moiré by interrupting a part of the interference pattern by the absorption grating, and detecting this moiré image using a detector. The information on the phase of the subject can be acquired by analyzing this moiré image. The imaging using a phase of light like this is generally called phase imaging (x-ray phase imaging if an x-ray is used).
However what can be directly analyzed by the interference pattern is a spatial differential amount of a phase of light that is changed by transmitting through the subject (also called differential phase image or shear image).
Since spatial differentiation has the effect to enhance edges, a differential phase image is used for enhancing an image of a subject in the field of optical microscopes or the like. An original phase can be calculated based on the differential phase image, so as to acquire the original phase image.
NPL 1 discloses an x-ray phase imaging method using two-dimensional Talbot interferometry. In concrete terms, a differential phase image in the X direction and a differential phase image in the Y direction are acquired from an interference pattern generated by two-dimensional diffraction grating, and a phase image is calculated by performing Fourier-domain integration method on these differential phase images.